Human lymphoblastoid B cells are a subset of highly activated B cells which are induced by in vivo immunization. In vitro these B cells produce antibody without the need for T-cell help or mitogen stimulation, and the majority of the antibody production is complete by day 3 of culture. In the past year, we found that the antibody-producing capacity of these cells can be reduced in vitro by NK cells and a separate suppressor T-cell subset. In the coming year, we will determine whether all NK cells have this inhibitory capacity or, as suggested by our earlier studies, only a subset of NK cells performs this function. We will test this by selective removal and/or isolation of different subsets of NK cells using monoclonal antibodies with differing specificities. It is also clear from our studies that not all lymphoblastoid B cells are capable of being inhibited, and we will attempt to determine what are the unique properties of the susceptible B cells. In conjunction with these studies we will determine if the NK-\and T-cell suppressors recognize the same or different target structures. These studies will also be accomplished by the use of monoclonal antibodies directed at B-cell target structures as well as by the use of cold target cell competitions. (LB)